Field of the Invention
This invention relates to a sheet conveying apparatus, a control method of a sheet conveying apparatus, and a control program of a sheet conveying apparatus. More specifically, this invention relates to a sheet conveying apparatus, a control method of a sheet conveying apparatus, and a control program of a sheet conveying apparatus which can recognize a state of sheet conveying with more precision.
Description of the Related Art
Some image forming apparatuses such as MFPs (Multifunction Peripherals), facsimile devices and copying machines or scanner devices have a sheet conveying apparatus, such as an ADF (Auto Document Feeder) or the like. An image forming apparatus having a sheet conveying apparatus can automatically execute printing on sheets, with conveying a plurality of sheets stored in a paper feeding cartridge one by one. A scanner device having a sheet conveying apparatus can automatically read document images by a scanner, with conveying a plurality of documents set on a document tray one by one.
Multiple feed may occur in a sheet conveying apparatus at rare intervals. Multiple feed is a phenomenon in which more than one sheets are overlapped each other and conveyed simultaneously. To prevent the multiple feed, a technique is proposed. According to the technique, a sensor which electrically or mechanically detects sheets passing through a conveying path is provided in the conveying path, and a multiple feed is detected based on the detection timing of the sensor. According to another technique proposed, an ultrasonic wave sensor (a multiple feed detection sensor of an ultrasonic wave type) is provided in a conveying path, and a multiple feed is detected based on the change in the quantity of transmission of ultrasonic waves which is transmitted through a sheet.
FIG. 32 shows a conventional technique using a detection sensor for detecting sheets passing through a conveying path. In FIGS. 32 to 37, arrow AR101 shows a conveying direction of documents in the conveying path.
Referring to FIG. 32, document tray 1005 holds a plurality of documents (sheets) DT. From the upstream side to the downstream side in conveying path TR, upstream side roller 1001, upstream side sensor 1002, downstream side sensor 1003, and downstream side roller 1004 are placed in this order. A plurality of documents DT stored in document tray 1005 are fed one by one into conveying path TR by upstream side roller 1001. Documents fed into conveying path TR are conveyed along conveying path TR, by each of upstream side roller 1001 and downstream side roller 1004.
The sheet conveying apparatus predicts the location of the document being conveyed, by using a rotational speed of upstream side roller 1001 with reference to a clock time when upstream side sensor 1002 detects the anterior end of a document (a clock time when upstream side sensor 1002 is turned on). Then, the sheet conveying apparatus detects the presence or absence of a multiple feed, based on whether upstream side sensor 1002 detects the posterior end of the document (whether upstream side sensor 1002 is turned off) or not, at the estimated time when the posterior end of the document is expected to pass through upstream side sensor 1002.
FIG. 33 shows a conventional technique using an ultrasonic wave sensor.
Referring to FIG. 33, document tray 1005 holds a plurality of documents DT. From the upstream side to the downstream side in conveying path TR, upstream side roller 1001, ultrasonic wave sensor 1006, and downstream side roller 1004 are placed in this order. Ultrasonic wave sensor 1006 includes transmitting unit 1007 for transmitting ultrasonic waves as shown by arrow AR102, and receiving unit 1008 for receiving the ultrasonic waves from transmitting unit 1007. Transmitting unit 1007 and receiving unit 1008 face each other, interposing conveying path TR. A plurality of documents DT stored in document tray 1005 are fed one by one into conveying path TR by upstream side roller 1001.
When a document passes the detecting location of ultrasonic wave sensor 1006, a part of the ultrasonic waves from transmitting unit 1007 reflect by the document. In consequence, the intensity of the ultrasonic waves being received by receiving unit 1008 decreases. Herewith, the sheet conveying apparatus detects the passage of the anterior end of the document through the detecting location. When a plurality of documents simultaneously pass through the detecting location of the ultrasonic wave sensor, the ultrasonic waves reflect by the plurality of documents. In this case, the intensity of the ultrasonic waves being received by receiving unit 1008 further decreases. Herewith, the sheet conveying apparatus can detect the occurrence of the multiple feed. The sheet conveying apparatus can also detect the anterior end of the preceding document and the deviation amount.
Document 1 below discloses a technique using an ultrasonic wave sensor, for example. In the Document 1 below, by using an ultrasonic wave sensor, the sheet conveying apparatus detects the leading end of a sheet of paper being conveyed, the leading end of the multiple feed part, the posterior end of the multiple feed part, the posterior end of the document, or the like. Herewith, the sheet conveying apparatus calculates the overlapping width of the multiple feed, and switches the multiple feed separating process after detecting the multiple feed, in response to the overlapping width.
[Document 1] Japan Patent Publication No. 2008-120493
The conventional technique using a detection sensor, and the conventional technique using an ultrasonic wave sensor have problems as follows.
FIGS. 34 and 35 are for explanation pertaining to problems of a conventional technique having a detection sensor for detecting sheets passing through a conveying path.
Referring to FIG. 34, it is assumed that the deviation amount is small (the overlapping width of the documents is large) in case of the occurrence of the multiple feed. In this case, the posterior end of document DT1 and the posterior end of document DT2 almost simultaneously pass through the detecting location of upstream side sensor 1002, at the estimated time when the posterior end of document DT1 is expected to pass through the detecting location of upstream side sensor 1002. Therefore, according to the conventional technique using the detection sensor, the occurrence of the multiple feed can not be detected in case that the overlapping width of the documents is large.
Referring to FIG. 35, in the conventional technique, the presence or absence of the multiple feed of document DT1 can not be detected until the estimated time when the posterior end of document DT1 is expected to pass through the detecting location of upstream side sensor 1002. Therefore, when the sheet conveying apparatus detects the occurrence of the multiple feed, the anterior end of document DT1 reaches at the inner part of the sheet conveying apparatus (the location downstream from downstream side roller 1004). Since the image reading of the anterior end of the document DT1 has already started, the read image data should be deleted. Further, the anterior end of document DT1 is damaged.
FIGS. 36 and 37 are for explanation pertaining to problems in a conventional technique using an ultrasonic wave sensor.
Referring to FIG. 36, ultrasonic waves have both directional characteristics and characteristics of diffraction. Hence, even though the anterior end of document DT1 reaches the detecting location of ultrasonic wave sensor 1006, the ultrasonic waves from transmitting unit 1007 sneak around to the back of the anterior end of document DT1 and enter receiving unit 1008, as shown by arrow AR103. Namely, there is a time lag (a delay in response) between the clock time when the anterior end of document DT1 is detected (and the clock time when the occurrence of the multiple feed is detected) and the clock time when the intensity of the ultrasonic waves received by receiving unit 1008 decreases in reality. In consequence, in case that an ultrasonic wave sensor is independently used, the accuracy to detect the anterior end of the document and the starting location of the multiple feed is poor.
Referring to FIG. 37, when an overlapping quantity of document DT1 and document DT2 is small, the ultrasonic waves from transmitting unit 1007 sneak around to the back of the overlapping part of the documents, and enter receiving unit 1008, as shown by arrow AR104. In consequence, the intensity of the ultrasonic waves received by receiving unit 1008 almost does not decrease from the intensity with no multiple feed (from the intensity of the ultrasonic waves passed through a single sheet of a document). Hence, the presence or absence of the multiple feed can not be detected.